Present day wireless communication systems, such as WCDMA (Wideband Code Division Multiple Access) continue to evolve to support high bit rate applications. As data rates increase, so does interference and self-interference from the dispersive radio channels, which in turn severely limits performance. In order to combat these problems, advanced receivers for WCDMA terminal platforms and base stations are continually being developed and further improved. Consequently, in future versions of mobile communication systems like WCDMA, Interference Suppression (IS) will be used in order to achieve better performance in terms of e.g. peak data rates, coverage, system throughput and system capacity.
Typically, the user equipment (UE)s of the WCDMA uplink (UL) are subject to so called fast inner loop power control. These power control loops steer the powers of each user, to achieve a set signal to interference plus noise ratio (SINR) target for the connection of the UEs. This in turn means that all power control loops are coupled nonlinearly, via the SINR (Signal and interference plus noise ratio) measurement (the so-called party effect). In other words, if one UE feels the need to increase its power, as a result all other UEs will feel a need to further increase their power. It is well established in the literature that the loops stay stable as long as the uplink (UL) is operating below its pole capacity. However, when the system is close to the pole capacity, stability is reduced and so called power rushes can occur. This is a very significant problem in WCDMA since the power control loops are very fast and capable of stepping up the UE power with as much as 1500 dB/second. Means that prevent such power rushes are therefore a necessity in case the UL of the WCDMA system is to be operated close to the pole capacity.
In order to alleviate the effects of the above described power surges, one commonly used method is the so called fast congestion control (FCC). The method acts to interrupt the power control loop in case of occurring power surges, thereby preventing UEs from trying to increase their respective power. FCC may use various measurements to achieve its goal, however a high bandwidth measurement of, or associated with, the WCDMA UL load is a necessary ingredient.
However, for systems utilizing interference suppression capable receivers a number of problems occur that prevent FCC from being an effective means to prevent power surges. Some of these problems include:
A first problem is caused by the fact that with IS receivers the power control loops are closed after IS processing. There is no established way to measure or estimate the load after IS.
A second problem is that FCC will become too conservative in case the load measures available for the WCDMA UL, without IS receivers are used. This is because a higher load than what is seen after IS is used for FCC.
A third problem is that IS receivers are sometimes more sensitive to the overall interference situation of the WCDMA UL. The stability of the UL power control loops of IS receivers can therefore be foreseen to become more prone to power runaway, than the loops of conventional receivers.
A fourth problem is the fact that in order to maximize the throughput more and more aggressive scheduling is used; a fact that further increases the risk of power rushes in the future.
Therefore, the need for FCC is deemed to become increasingly important with the introduction of IS receivers in the WCDMA UL.
Consequently, there is a need for methods and arrangements enabling taking interference suppression into account when determining load for use in fast congestion control in WCDMA systems.